The present invention relates to an improved method and apparatus for heating aggregate and the like.
In the usual method for producing asphalt, aggregate material is conveyed through a heating chamber where it is heated to a desired temperature before its incorporation into asphalt. Heat is supplied to the heating chamber by a combustible fuel mixture formed in a mixing unit from a stream of fuel and a stream of forced air, and injected from this unit into the chamber. Typically, aggregate-heating systems of this type are automated to the extent that the volume-flow rates of fuel and air introduced into the mixing unit are adjusted automatically to maintain the temperature of heated aggregate being discharged from the chamber substantially constant.
A significant economic factor in asphalt production is the cost of fuel used in operating the aggregate-heating system. Typical heating systems which are widely used in the industry consume the fuel equivalence of about three gallons of liquid fuel per ton of aggregate heated. At the usual aggregate-processing rates, this translates to a fuel consumption rate of several hundred gallons of liquid fuel per hour of operation. It is apparent that a substantial reduction in the fuel consumption rate in such a system would produce considerable cost savings, and environmental benefits as well.
It has been proposed heretofore to increase the efficiency of an aggregate-heating system by humidifying the air introduced into the mixing unit. This has been done, in a system employing a high-volume forced air blower for introducing air into the mixing unit, by placing the intake side of the blower in communication with a large-area water evaporation tank. Water vapor drawn into the blower is introduced thereby into the fuel mixture. Alternatively, it has been proposed to bubble air drawn into such a blower through a water tank, to entrain water vapor in the air stream introduced into the mixing unit. In both methods, the amount of water vapor which can be drawn into the blower is limited by the evaporation rate of water, which, under normal conditions, is insufficient to produce significant fuel efficiency increases in an aggregate-heating system. Further, the volume rates of water drawn into the blower cannot be easily regulated.
One object of the present invention, therefore, is to provide, in an aggregate-heating system, a water-feed apparatus which effects a significant improvement in fuel efficiency in the system.
A related object of the invention is to provide such an apparatus which can be regulated to introduce, into a blower in an aggregate-heating system, a volume rate of water which maximizes fuel efficiency in the system.
Still another object of the invention is to provide such apparatus which is simple to install and operate.
Providing a method of increasing the fuel efficiency in an aggregating-heating system, by introducing a controlled amount of water vapor into the system, is yet another object of the invention.
The water-feed apparatus of the invention includes a water-spray device for producing a fine-particle, or atomized. spray which is injected into the air-flow stream created by the blower in an aggregate-heating system. The spray device is supplied by streams of water and pressurized gas. In a preferred embodiment of the invention, the pressure of gas supplied to the spray is regulatable to adjust the volume-rate of water introduced into the blower. The atomized spray preferably is introduced into the air-intake opening in the blower.
In the method of the invention, an aggregate-heating system is adjusted so that a substantially constant-quantity rate of aggregate is heated by a fuel mixture characterized by a substantially constant fuel-flow rate. While the temperature of the heated aggregate is being monitored, a fine-particle water spray is introduced into the air stream of the blower, and the volume rate of introduced spray is regulated until a maximum monitored aggregate temperature is observed. The amount of fuel supplied to the system is then adjusted to produce a moisture-containing fuel mixture which effects heating of the aggregate to a desired temperature.